Control switches



April 1958 E. E. o. ENGEL ETAL 2,830,160

CONTROL SWITCHES Filed July 7, 1954 Q 2 Sheets-Sheet 1 #vvnvroes lee/visiezo swan.

rnn/vc/s me. @1566 ATTORNEYS April 1958 E. o. ENGEL EIAL, 2, 0,160

CONTROL SWITCHES Filed July 7, 1954 2 Sheets-Sheet 2 A'E/VSST 0. IV6L l'RANC/S W G. 6 1885 ATTORNEYS .CDNTROL SWITCHES Ernest E. 0. Engel and Francis W. G. Gibbs, Boreham Wood, EistremjEngl-and, 'assignors' to Engel & Gibbs Limited, Elstree, Engiand' Application Juiy 7, 1954,8eriai N 441,878 Claims priority, application Greatv Britain July 17, 1953 3 Claims. (Cl.- 230-152) This invention relates tocontrol swiitches for the making and/ or breaking of electrical circuits.

The invention relates in particular to the 'so-called mercury type control switches in which an'electrical conductive 'substa'ncein 'fluid.form,"such as mercury, is contained in a sealed tube under vacuum or other desired conditions such as an inert gas. Two o'r'more electrodes projecting into the tube are usually provided and the the region of tendegrees. This lackof extreme sensitivity does not affect the normal industrial application of'the switches as the tilting movement is usually greatly in excess of ten degrees. The applicants have-realised however, that the switches couldbe morefgenerally used on specialised apparatus if the sensitiviity of theswitches could be increased. It is an important object. of the invention therefore, to provide an improved control switch of the mercury type which is extremely sensitive even to very small tilting'movements of the tube. a The elforts of the applicants to produce a more sensitive switch has now "led to the use of less mercury than is usual in the tube of the switch. It'has now been found that such an arrangement'has a disadvantage in that the reduced mass or the mercury may cause an occasional failure of the mercury to make a good electrical connection with the electrodes It is theretore a'further object of the invention to provide a control switch of the mercury type having improved electrodes .by which this-disadvantage is substantially overcome.

A recent important industrial application of mercury switches is the control of electrically operated gyroscopes. It has been suggested that mercury level switches-may be mounted on each gimbal of the gyro so that any tendency of the gyro axis to wander will tilt the corresponding switch to complete an electrical circuit operating the torque motors or other erection system of the gyro so that the wander of the gyro is counteracted.

Owing to the above mentioned disadvantages the results obtained have not beenrsatisfactory, as known switches are not suificiently sensitive. It is, theretore, a further object of the invention to provide a mercury type switch suitable for gyro control and sensitive to a wander movement of the gyro of a small fraction of a degree so that any tendency of the gyro axis to wander is immediately counteracted by the erection system.

It is of course well known to use gyroscopic units for the stabilising of ships, gun platforms on tanks and other land vehicles, and the present invention is most suitable for use with the gyros of such units. 7

' The application of the invention to the gyroscopic units of aircraft has however, presented further 'difiiculties mond file during manufacture. 7 'minute longitudinal grooves or scratches so produced in'thatthe use of mercury renders the units inoperative at temperatures below that at which mercury solidifies, i. e. about --39 C. At operational heights specified for most military'aircraft this temperature is frequently exceeded and .a-still further object of the invention is therefore to provide asensitive mercury level switch operative below the normal melting point of mercury and preferably to'a temperature of approximately .60 C.

According to the present invention there is provided a control switch comprising a sealed envelope, two or more electrodes projecting therein, and an electrical conductive substance ingfiuid form insaid envelope and movable-to complete or breakfel'ectrical continuity between the electrodes, wherein-the envelope is formedwith a matte or non-shiny track on its inner surface for the electrical conductivegsubstance. Preferablythe tub'e is roughened or ground and this may be obtained by the longitudinal rubbing of the surface of the tube by a dia- It is believed that the assist the smooth and even running ofthe mercury;

According to a. further aspect of the invention there is provided acontrol switch comprising a sealed envelope, two or' more electrodes projecting therein, and an electrical conductive substance in liquid form-in ,saidenvelope and movable to complete or break electrical continuity betweenthe electrodes, wherein the electrical conductive liquid mercury and a substance amalgamated therewith whereby the melting point of the amalgam is lower than 'that'of'pure mercury.

'One'such substance-is the element thallium and a preferred liquid includes 8% thallium amalgamated with mercury which has been triple distilled under vacuum.

Preferably the electrodes projecting into --the envelope are forrned with pointed contact portions to give a good electricalconne'ct'ion with the electrical conductive material. The electrodes are preferably of tungsten and the pointed ends are conveniently formed by grinding or by an electrolytic process in'which' the ends eaten away. v

'In' oneconstruction of a control switch according ,to the invention the envelope is providedwitha' rod electrode extending substantially along its lengthand there is an electrode at each end of'the switch. If desired one or more additional electrodes may bepositioned alon'g'the length of the rod electrode.

'In a second construction, the envelope is'provided with apair of electrodes at each of its ends. 7 j

In a third construction, the envelope has a pair of spaced rods extending along its length, one of the rods being an electrode,-and the other being formed of an insulating material'and having a resistance wound thereon.

The envelope may be' a straight or curved glass tube.

The control switches may be used for the control of gyroscopic units and the invention particularly provides an artificial horizon having two control switches, one responsive to movement of theunit in the pitching plane and the other to movement of the unit in the rolling plane. Preferably the control switches are connected to the corresponding torque motors of the erection system.

In order that the invention may be fully understood, some preferred embodiments will now be described by way of example with reference to the accompanying diagrammatic drawings, in which:

Figure l is a perspective view of a typical controlswitch according to the invention;

Figure 2 is a similar view partly in-section to show are gradually the matte ornon-shiny track on the inner surface of the EPatented Apr. 8, 1958 section ofza further embodiment;

artificial horizon.

Referring now to Figures 1 to 4 of the drawings there is shown a control switch comprising a glass tube 11 about an inch long and a quarter of an inch in'diameter. Thetube 11 is preferably straight in its longitudinal direction as shown in Figures 1 to 3, but if desired, it may be curved as shown in Figure 4 to suit various requirements regarding sensitivity and range of angular movement. 1

During manufacture thetube 11 is roughened or ground throughout its length on one half of itsinner surface 12. This renders the lower half of the tube opaque as shown at 13a in Figure, 1. This roughened surface 12 forms a running surface for an electrical conductive liquid 14 (to be hereinafter described) and is formedduring the manufacture of the switch by means of adiamond file which is rubbed upon the internalsurface of the tube 11. The roughened surface 12 includes minute'longitudinal scratches 13 and it is believed that these greatly assist in the production of the surface which will ensure the smooth and even running of the liquid 14.

The electrical conductive liquid 14 comprises an amalgam of mercury and thallium. The amounfof thallium is preferably about 8% and the mercury is triple distilled under vacuum- The amalgam so .formed is fluid at normal temperatures and solidifies 'at'about 58 C. which is well below that for pure fmercury (about -.-39 C.) and well below the operational requirements of most military andcivil equipment.

The' desired quantity of amalgam 14 is inserted in the tube 11 and'the tube is then evacuated and sealed, great.

care being taken that no contact is made with the air by the amalgam.

Prior to. this step various electrodes are sealed into the walls of the tube 11. 7

In its most simple form the tube 11 is provided with a rod electrode. 15 extending the length or substantially the length of the tube 11 approximately along its longitudinal axis. This electrode 15 is conveniently connected at its outer end to a source of electrical energy by a wire 16.

Below the rod electrode 15 (i. e. on that side of the rod 15 adjacentthe roughened wall 12 of thetube), there is mounted a pair of electrodes 17, 18, parallel with the rod electrode 15 and extending into the tube 11 one from each end 19, respectively. The electrodes 15, 17 and 18 are made from tungsten and the two lower electrodes 17 and 18 have contact portions 21, 22 in the form of sharply pointed ends. Such contacts 21, 22 ensure a good connection with the moving mass of amalgam 14 and are produced by treatment in an electrolyticbath or by grinding.

The amount of amalgam'14 in the tube 11 is such that with the tube level (Figure 3) the mass of amalgam 14 is spaced from the two pointed electrodes 17, 18 but is in contact with the rod electrode 15.

t The two pointed electrodes 17, 18 are connected by wires 23, 24, into various control circuits? as desired and in operation any tilt of the tube 11 in one direction or the other will cause the mass of amalgam14 to run into one of the pointed electrodes 17, 18 and so complete the corresponding circuit. The amalgam 14 is of course, at all. times in running contact with the rod electrode l5.

The preferred use of the switch is for the control of 4 gyroscopic units, such as directional gyros, and artificial horizons on aircraft.

One such application of the invention is shown in Figure 9 in which the control switches control the operation of the erection system of an artificial horizon.

The artificial horizon includes a vertical gyro mounted in a support which includes an inner gimbal 31 and an outer gimbal 32.. An erector system precesses the gyroscope axis to the vertical and includes a pitch precessing motor 33 with its axis extending fore and aft of the crafton which the gyroscope is mounted, that is on the gyroscopes bank axis, and a bank precessing motor 34 with its axis extending transversely of the craft, that is on the gyroscopes pitch axis. The gyroscope is housed within a casing 35 and is connected with an electrical supply by leads 36, 37.

Two control switches 38,39 are mounted on the inner gimbal 31 and are connected to the electrical supply by leads 40, 41 respectively. The leads 40, 41 are connected to the rod electrodes 15 of the switches. The electrodes 17, 18 ofthe' switch 38 are connected by leads 42, 43 to the motor 33 so that the motor 33 will be energised in one orthe other direction of rotation depending upon I the tilting of switch 38. The switch 38 is mounted on the gimbal 31 along the fore and aft of the craft and any deviation of the gyro from thevertical'in the fore and aft direction will therefore operate the switch 38 to close the circuit to the motor 33. The motor 33 applies the correct couple to the gyro axis to cause it to precess and return to its vertical position. Similarly the elec trodes 17, 18 of the switch 39 are connected by the leads 44, 45 to the torque motor 34 so that the motor will be energised by the switch upon a deviation of the gyro from the vertical in the transverse direction.

The switches 38, 39 will therefore operate to correct any tendency ofthe gyroscope axis to wander from the true vertical due to the effect of the earths rotation, fric- .tion etc.. The switches are extremely sensitive and a tilttached to the outer gimbal 32.

During turns, the switch 39 mounted parallel with the pitch axis of the aircraft issubject to the action of centrifugal force and thus may operate to give errors in the control of the gyro. These errors may be avoided by means of the known pitch-bank systems of erection switchingin which control of the torque motor 33 operating on the roll axis is transferred to the pitch axis control system.

The simple control switches as described above may in some circumstances sutfer the disadvantage of hunting of the gyro under control.

This defect can be corrected by providing the tube 11 as shown in Figure 5 which has a plurality, for example four, additional pointed electrodes 46, 47, 48, 49 extending downwardly from the upper surface 50 of the tube at the side of the rod electrode 15 and to a point just below it. The additional pointed electrodes 46 to 49 are spaced along the length of the tube and are arranged so that movement of the amalgam along the tube in one direction progressively brings the series of electrodes into electrical connection one after the other with the rod electrode 15. It will be appreciated that the electrodes can be connected in circuits with the same torque motor, each circuit including a resistance of different value so that successive electrodes from the centre of the tube will produce currents of decreasing value for loading the motor to produce a more accurate and gradual control.

It is preferred to mount the multiple electrode switch of Figure 5 and its resistances in a panel so that the device can be fitted as a unit. A cover plate, for example of plastic, can be fitted to the panel to prevent damage and the entry of dirt. In certain instances such as the control of automatic pilots, the panels are provided with a series of recesses adapted to take two switches or more at right angles to each other together with their resistances.

In a further modification shown in Figure 6 the resistances are provided internally of the tube. In this form of the invention the tube 11 has two rods 15a, 51 extending along its length parallel to each other, one of the rods being the same as the rod electrode 15 referred to above. The other rod 51, which may be of any suitable insulating material is connected with the torque motors by the.

lead 52 and is provided with a wound resistance 53 thereon. It will be appreciated, therefore, that movement of the amalgam 14 will have the efiect of connecting the rod electrode in circuit with the torque motor through a varying resistance.

In a further modification shown in Figure 7 a tube 11 can be produced without the rod electrode. In this arrangement the tube is provided with a pair of pointed electrodes 54, 55 at each end, one electrode say 54, of each pair being connected to the source of electrical energy. 1

A still further form of switch shown in Figure 8 provides means for the insertion of a higher current into a completed circuit as is required, for example, for the rapid erection of a gyro under certain operational requirements.

The gyro is conveniently provided with a rapid erection button at the side of the unit and depression of this button is arranged to complete a circuit which connects a rapid erection electrode 56 in the switch tube 11 with an electrical supply source of greater voltage or current.

The rapid erection electrode is pointed at 57 as shown and depends from the upper surface of the tube at approximately its mid-point. If desired the rod electrode 15 (if fitted) can be split at this point but the electrodes must of course all be positioned so that contact can be made with both the rapid erection electrode 56 and one of the circuit electrodes 17, 18 by the amalgam-14 during at least a certain range of tilt of the tube.

The control switch described above have of course industrial applications too numerous to mention but it will be appreciated that their use is invaluable where an ex tremely sensitive and accurate electrical control is required. Due to the particular amalgam used the control switches are not subject to errors due to temperature variation and they are in fact fully and accurately operational in a temperature range starting at the abnormally low value of 58 C.

We claim:

1. A control switch comprising a tubular glass envelope, said envelope sealed at each end and under vacuum, a plurality of sharply pointed electrodes projecting into said envelope, an electrical conductive substance in fluid form in said envelope and movable to complete or break the electrical continuity between the electrodes, and a plurality of longitudinal scratches on the lower half of the inner surface of said glass envelope extending the length thereof to form a track for said conductive substance whereby the smooth and even running of the electrical substance is insured.

2. A control switch comprising a tubular glass envelope, said envelope sealed at both ends and under vacuum, a plurality of electrodes projecting into said envelope, at least one electrode being sharply pointed, at least one electrode being of rod-like form, an electrical conductive substance in fluid form in said envelope and movable to complete or break electrical continuity between said rod-like and sharply pointed electrodes, and a plurality of minute longitudinal scratches on the lower half of the inner surface of said glass envelope extending the length thereof to form a track for said conductive substance.

3. A control switch comprising a tubular glass envelope, said envelope being sealed at both ends and under vacuum, a pair of spaced rods extending the length of the envelope, one of the rods being an electrode the other rod being formed of insulating material and having a resistance wound thereon, an electrical conductive substance in fluid form in said envelope and movable to complete or break electrical continuity between said electrode and wound resistance, and a plurality of minute longitudinal scratches on the lower half of the inner surface of said glass envelope extending the length thereof to form a track for said conductive substance.

References Cited in the file of this patent UNITED STATES PATENTS 898,766 Mott Sept. 15, 1908 1,144,973 Warren June 29, 1915 1,871,177 Held Aug. 9, 1932 2,033,372. Bear et al. Mar. 10, 1936 2,232,590 Craig Feb. 18, 1941 2,348,950 Anderson May 16, 1944 2,376,377 Muma et al. May 22, 1945 2,626,997 Thomas Jan. 27, 1953 2,768,259 Bild et al. Oct. 23, 1956 

